Anne hasn't mentioned any plans to write another Freedom book in the past few years, so I don't think we'll be getting a sequel to wrap things up.

Usually her non-Pern sequels have happened because she's had a new idea for a plot to write....so no brilliant idea, no book. Also, her main publisher (Del Rey) is most interested in her writing Pern, as that's what sells the best. If you did want to petition anyone, I'd go for the publisher because if they actually asked her to write one, she probably would.